The Fate of Shrimp Is Written in Cod!
Total Page:16
File Type:pdf, Size:1020Kb
Population growth and range expansion – the introduced red king crab off Northern Norway Carsten Hvingel1, Jan H. Sundet1, Einar M. Nilssen1, Ann Merete Hjelset1 and Franz Mueter2 1Havforskningsinstituttet—Institute of Marine Research, P.O. Box 6404, N-9294 Tromsø, Norway. 2College of Fisheries and Ocean Sciences, University of Alaska Fairbanks, Juneau, Alaska King crab – off northern Norway Survey stations King crab is an introduced species to the Barents sea Found in coastal areas, in Norway primarily in four Laksefjord Tanafjord fjords Porsanger fj. At first a pest, later a valuable fishery resource (or both?) Varangerfjord Norway Russia Challenges in King crab management How much can • Short term: we fish now? • Setting the annual quota What investments are • Longer term: warranted? • Scope of the fishery? Will there be a • Ecosystem effect price to pay? • Spreading Build population dynamics model V ij = N fa 22VN + i N max (,i ) = −+ 2 R Sexp( a bS c f( X , , a , g ,...,) ij ∑ i i ij,, ij , 1 N N ∑ j 2 ∑ j N 2 j VN j maxi i N = VNmax N j Vij ij, ∑ 22N (,j ) + = 22+ N fa(,ij, ) ij N fa V ∑ N j j Porsanger Tana Modelling the population dynamics Lakse Varanger Logistic 120 population growth model 100 80 Sequential colonization: Four fjords 60 repeating the same Population size Population 40 “experiment”…. 20 ..each carry some unique 0 information 0 20 40 60 80 100 120 about model Time parameters. Model Varanger Tana Laksefjord Porsanger Hierarchical model ..allows us to dN N “borrow jj=Nr1 − Logistic growth (j indexes strength” for jjfjord 1 to 4) estimation. dt K j Ctj 2 MSYj P tj P tj Discrete stochastic version PPt+1, j=− tj +1 −⋅ exp(ν tj ) standardised to Nmsy NNMSY,, j MSY j 2 MSY K K MSY MSY Hyper Local (fjord) parameters parameters K MSY K MSY K Informative priors MSY sample: 10000 1.0 Based on MSY from Bristol Bay 0.5 0.0 0.0 2.0 4.0 Tonnes/km2 q sample: 10000 3.0 2.0 1.0 Expert knowledge 0.0 0.0 0.5 1.0 Catchability (proportion) Porsanger Tana Results: by fjord Lakse Varanger 2.5 2 =1) Bmsy ( 1.5 biomass 1 Relatime 0.5 0 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 2025 Varanger fjord Tana fjord Lakse fjord Porsanger fjord Results: total 2.5 A 2.0 1.5 Bmsy 1.0 Biomass(index) MSY 0.5 Blim 0.0 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 4 B 0.0 1.0E+3 2.0E+3 3.0E+3 3 Tonn 2 Flim Fmsy 1 Fishing mortality (index) mortality Fishing 0 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 Year 1.2 Total stock Varanger fjord 4000 1.0 0.8 3000 Some diagnostics: 0.6 Estimated biomass (inter quartile range, grey) 2000 0.4 vs. 0.2 observed (black line) 1000 1995 2000 2005 2010 2015 2020 1995 2000 2005 2010 2015 2020 1.2 1.2 Tana fjord Lakse fjord 1.0 1.0 0.8 0.8 0.6 0.6 0.4 0.4 Index of biomass of Index 0.2 0.2 1995 2000 2005 2010 2015 2020 1995 2000 2005 2010 2015 2020 1.2 1.2 Porsanger fjord Offshore 1.0 1.0 0.8 0.8 0.6 0.6 0.4 0.4 0.2 0.2 1995 2000 2005 2010 2015 2020 1995 2000 2005 2010 2015 2020 Year Year You are here New areas: e.g. Balsfjorden Scope of a new fishery any before much MSY Balsfjord data is available.. 0.0 20.0 40.0 Tonnes 2.5pc median 97.5pc MSY Balsfj. (t) 14.1 21.8 37.7 Termal habitat, adults ..found across -1.8 to 18 oC.. Eastern Bering Sea Probability of occurrence Bottom temperature (oC) Termal habitat, adults Commercial densities across 0-7 oC Eastern Bering Sea Log(CPUE) Density Bottom temperature (oC) Temp oC Distribution 2000 1960-70 2010 1990 2020 Densities of Tromsø commercial interest down to 2030 65 oN.. 2040 ..but crabs may still be found 2050 further south. But what about further north? Temp oC Distribution 2030 Until now, the prevailing currents have 2025 hindered advection north.. ..now as the crab has reached “the 2000 junction point”, 1960-70 2010 1990 probability of northwards 2020 larval drift is Tromsø much higher 2030 2040 2050 Conclusions • Bayesian Hierarchical models are powerful, particularly when data are limited. • Scope and stock development in newly colonised fjords can be estimated before a data collection program is established. • Production in crab habitat: 115-225 kg males>130mm pr. km2 pr. year (80 pct.). • Continued expansion of KC distribution upstream is expected – potential for high (commercially interesting) densities down to about 65oN, but KC will also be found further south. • As KC has now reached the junction of the coastal current, the potential for larval advection northwards is increased – adult KC may be found on Svalbard within 5- 10 years. .